Research on shale gas transportation and apparent permeability in nanopores

Shale gas transport mechanisms in matrix nanopores include the Knudsen diffusion, transition diffusion, slip flow of free gas and surface diffusion of adsorbed gas. Previous research focused on shale gas Knudsen diffusion, slip flow and surface diffusion. In this paper, we present a shale gas mass flux model for the shale formation matrix that incorporates transition diffusion, slip flow and surface diffusion. A set of shale formation data was used to analyse the sensitivity of the gas mass flux to the pore radius and pressure for each gas transport mechanism. The results show that each gas transport mechanism mass flux contribution varies with the pore radius and pressure. The results of the gas mass flux sensitivity analysis are as follows: (1) the slip flow mass flux increases with increasing pore radius and pore pressure, (2) the surface diffusion mass flux decreases with increasing pore pressure and pore radius, and (3) the transition diffusion mass flux decreases with increasing pore pressure and has only a slight dependence on the pore radius. Furthermore, the gas type notably influences the apparent permeability. We recommend this model for the description of the shale gas mass flux in matrix nanopores. It provides insights into the effects of transition diffusion, slip flow and surface diffusion on the shale gas transportation in nanopores.